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Written by Jason Keeping
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Wednesday, 30 April 2008 19:00 |
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Page 3 of 3
SIDE BAR:
Conformal Coating CharacteristicsAcrylic resin (AR): Acrylics are fairly easy to apply and dry rapidly, reaching optimum physical properties in minutes, while providing a long pot life. Furthermore, acrylics have good humidity resistance, are low exothermic and give off little or no heat during cure, eliminating damage to heat-sensitive components, and do not shrink due to the solvent evaporation process during cure. Their main disadvantage is solvent sensitivity, but this is also an advantage, as it makes them the easiest coatings to rework.
Urethane resin (UR): Polyurethane coatings are available in both single- and two-part formulations. Both formulations provide good humidity and high chemical resistance. Due to these variations, some polyurethane coatings are easy to apply and cure rapidly, with other materials more difficult to apply because of their shorter pot life. With their wide range in good-to-excellent material properties, these characteristics also become their drawbacks in that chemical and mechanical removal techniques may become difficult and costly.
Epoxy resin (ER): Epoxies are more complicated to apply than other materials because of their shorter pot life since they are usually available only as two-part compounds. Furthermore, as a result of their cross-linking design, they provide average humidity resistance and high chemical resistance compared to other coating materials. However, their strength versus other coating materials is their abrasion resistance, but this also adds to their rework complexity, as chemical removal may attach to epoxy-coated components and the board itself and cannot easily be removed via mechanical methods due to abrasion resistance.
Silicone resin (SR): Silicones are a different form of coating, compared to other materials, with their main advantage being resistance to higher continuous temperatures and thermal expansion properties. Furthermore, silicones have high humidity resistance, and thanks to their 100%-solids design, have extended pot life, providing a fairly easy application and quick drying. Their main disadvantage is abrasion resistance and rework complexity. With the abrasion resistance a disadvantage, this should lead to lower rework complexity. However, the rework disadvantage is not in the coating removal, but rather the removal of residues that may be left from the coating.
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Last Updated on Friday, 18 July 2008 09:34 |
